1. Field of the Invention
The invention relates to an image formation apparatus and, more particularly, to an image formation apparatus having a plurality of development units.
2. Related Background Art
In conventional color copying apparatus and color printers, development units are moved by a rotating or elevating method and only the development unit which is being used to develop an electrostatic latent image is closely adhered to a photo sensitive material.
Therefore, a development bias power source is held in a connecting state with all of the development units. However, after that, development units of a fixed type have been devised in order to realize a high copying speed and a high image quality.
According to the conventional apparatuses, it is very difficult to move the development units which occupy considerable volume and weight in the copying apparatus at a high speed without generating a vibration which causes of deterioration of the image.
According to the rotating method and elevating method, there are problems in that not only is a construction of the development units complicated but also a space of the whole development units is large.
When the fixed type is used, since all of the development units face the photo sensitive drum, it is necessary to control at a high speed the AC component and DC component of a development bias which is applied to a development sleeve so that the toners of the development units which are not being used for development are not adhered to the photo sensitive material. It is necessary to provide a development bias power source for each development unit.
Since the development bias power source is constructed by multiplexing a DC high voltage to an AC voltage, an AC high voltage transformer, a DC high voltage transformer, their control circuits, and the like are fairly expensive. There is a problem in that a construction including a number of power sources equal to the number of development units provided results remarkably raises the cost of the apparatus.